Natural Zeolites as substrates for photocatalysts

Abstract

Ti02 is currently considered the most promising catalyst for the photocatalytic degradation of organic compounds owing to its suitable band gap energy for redox reactions, mechanical and chemical stability, environmental friendliness, low cost, and convenience of preparation. However, there remain further technological problems, which may include easy separation of the catalyst and improvement of adsorption properties for organic molecules at low concentrations in the media. Besides the electronic modifications to make Ti02 visible light active and enhancing its photoactivity new investigations have been devoted in searching for the suitable substrates to support nano Ti02 in order to improve the recovery efficiency and adsorption capacity. The combination of zeolites and photochemistry has recently shown excellent results due to the special structure of the zeolites that helps a better use of the solar energy improving the selectivity of the chemical reactions carried out. There are several reports on the preparation of Ti02 confined nanoparticles in synthetic zeolites. The aim is mainly to use hydrophobic zeolites in arder to favor the adsorption of the organic pollutants. However, very few reports are found in the use of natural zeolites. In our previous collaborations with Addis Ababa University and the Geological Survey of Ethiopia, we devoted big efforts in locating and analyzing deposits of natural zeolites in the country. Among the samples identified sorne of them possess interesting chemical compositions that may lead to direct photocatalysts with very little modifications.